Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the leading "[read]" tag simply restates structured data. The description adds no behavioral detail beyond the schema, such as ordering, pagination limits, or whether the filtered lookup is exact-match or partial.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

One clause plus one parameter note, no filler or repetition. It is front-loaded with the resource being returned, though the extreme brevity leaves the description underspecified rather than optimally sized for a three-parameter list tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple read-only list tool with no output schema, the key gaps are pagination semantics and result ordering/format, neither of which is covered. The one filter parameter is addressed, and annotations cover the safety profile, so the definition is minimally workable but not complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0% for three parameters, so the description must compensate and only partly does: it explains that `sms_optout_msisdn` narrows the result to a single number, which is genuinely useful. `page` and `per_page` are left completely unexplained, so two of three parameters carry no semantics anywhere.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The fragment "Numbers on the opt-out list" identifies the resource (SMS opt-outs) and implies a listing, but the verb is only implied by the tool name and no distinction is drawn from the nearby list_voip_optouts sibling. An agent can guess the purpose, but the description does not itself state that this retrieves a paginated collection of numbers.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no statement of when to use this versus alternatives such as list_voip_optouts or the SMS message/campaign listing tools, and no mention of prerequisites or typical workflows. The only guidance is the implicit 'pass the msisdn to narrow', which is parameter behavior rather than usage selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.